I'm using XNA, and I'm well versed with the skinnedModel sample. I'm starting to make my own models and animations. I'd like to be able to take animations that apply to different, independent body parts and combine them. For example:

Let's say I have some animations for my characters body:

running

walking

standing

I also have some animations for my characters face:

frowning

smiling

Ideally, I'd like my character to have any facial expression when doing any action. So, they could be:

walking while smiling.

walking while frowning.

running while smiling.

running while frowning

... and so on ...

However, I'm not sure how I should best manage this. I know that I could make N*M different animations (where N is the number of body animations and M is the number of face animations) and import them all, but this seems like a lot of work as the number of animations starts to increase.

Well, if you want something X and Y which can be combined freely, then you composition. For that you need to make parts X and Y independent from each other. Thus, as @GustavoMaciel suggests you need to separate face and body parts.

However the challenge here lies in the ability to combine parts smothly. So it can be quite possible that drawing all possible combinations can produce better results.